AthenaMP+AthenaServices: Support executing algorithms/sequences in AthenaMP during PreFork
This is an adaptation of @fwinkl's !55759 (merged) to generic AthenaMP. In a nutshell, this gives the possibility of executing certain algorithms/sequences during PreFork incident in AthenaMP. One can use this to execute the conditions algorithms before the first event, hence sharing the memory across workers even without FAFE.
Based on an 8 process, 10k event AODtoDAOD test w/ SharedWriter, vanilla MP uses about 2 GB/worker, executing conditions algorithms before the event loop this way reduces this to 1.5 GB/core, while FAFE still performs the best at 0.9 GB/worker:
Default
ExecAtPreFork
FAFE
We can take a look to see if there is any milage in adopting such an approach in other jobs such as derivation production.